Xanthation



2 Sheets-Sheet l Sept. 11, 1956 P. H. scHLossER ET AL XANTHATION Y Filed Feb. 29,l 1952 Sept. l1, 1956 P. H. SCHLOSSER ET AL 2,762,795

XANTHATION Filed Feb. 29. 1952 2 sheets-sheet 2 FIG. 3- y 46 49 45 42 vAcuuM a if \vAcuuM/ 44 4'7 I 43 @5. FIG.- 4

ELECTRONIC HEATING DEVICS United States Patent 'O XANTHATION Paul Henry Schlosser, Reid Logan Mitchell, and Robert F. Bampton, Shelton, Wash., assignors to Rayonier Incorporated, Shelton, Wash., a corporation of Delaware 'Application February 29, 1952, Serial No. 274,208

8 Claims. (Cl. 260-217) ment of a continuously moving web of alkali cellulosev produced by impregnating a web of dry cellulose pulp with a solution of caustic soda, and the removal of excess caustic solution as described and claimed in United States Letters Patent 2,614,102. The invention of said application effects a very uniform impregnation of the pulp web with caustic liquor and the removal of excess caustic, resulting in a uniform conversion of the cellulose to alkali cellulose.

ln accordance with this invention, we impregnate'rthe alkali cellulose web with a predetermined amountv of carbon bisulfide, distribute the carbon bisulde in a uniform manner through the web, remove a substantial part of the excess carbon bisullide, and heat the moving'web to complete the xanthation reaction, all in a continuous integrated operation. This invention achieves an etlicient conversion of the alkali cellulose to cellulose xanthate in a vrelatively short time, thus eliminating the tying up of a lot of expensive and space-occupying equipment. In short, our invention requires less equipment and space, and produces a better product in a shorter time.

In accordance with our invention, we prefer torimpregnate the alkali cellulose with liquid carbon bisulfde and store the moving web of cellulose xanthate under controlled conditions of temperature and pressure and then deposit lthe reacted Xanthated product in any convenient place for conversion into viscose. l

In carrying out our method, we may use a single web or a plurality of superposed webs of dry cellulose, and

we may treat the alkali cellulose with either gaseous or liquid carbon bisulfde. In one advantageousv embodiment, we pass two superposed webs through the operation and in the xanthation stage we separate the sheets to spray the inside surfaces with liquid carbon bisulfide and promptly bring the sheets together to trap the carbon bisuliide and minimize the loss of vapor.` To obtain uniform -distribution of carbon bisulde through the Webs and to= recover excess unreacted carbon bisulde, we pass the superposed webs between vacuum members.

In another embodiment of the invention, we apply continuously a predetermined dosage of carbon bisullide to the top surface of a web of .alkali cellulose while simultaneously applying vacuum to the underside of the web to draw the carbon bisulde uniformly into the alkali cellulose. The web of alkali cellulose uniformlyim- ICC pregnated with carbon bisullide may then be led into a heated reaction chamber to effect continuous xanthation of the web while the web is still intact. The carbon bisulfide impregnated web may also be slit into narrow ribbons, broken into fragments or otherwise distntegrated and then charged into a baratte, wet churn or other suitable xanthation reaction vessel.

In furtherance of the recovery of excess carbon bisulfide and to keep this dangerous compound out of the plant and atmosphere, we prefer to maintain entire sections of the xanthation equipment under sub-atmospheric pressure.

After the initial Contact of the alkali cellulose with carbon bisulde, we may heat the web in a chamber in which the web may have a long travel to allow completion of xanthation. We may heat this moving web of cellulose xanthate in any suitable way, as by means of infrared heating, induction heating, dielectric heating, radio frequency heating, and in this way accelerate the conversion to cellulose xanthate.

In one adaptation of our invention, we pass the web of alkali cellulose through a slitting means, such as intermeshing cylindrical shears, to slit the web longitudinally into strips of any suitable width, say, from 1A to 1 inch wide, prior to transfer to a suitable xanthate reactor.

The alkali cellulose web may be disintegrated by other suitable means such as a breaker of the hammer-mill type, a picker or a continuous shredding device. Such impregnated and disintegrated alkali cellulose is very suitable for loading into barattes, wet churns, or reactors of the inclined cylindrical cement-mixing type.

Alkali cellulose other than in web form may also be conveniently treated with carbon bisulde according to the method of the invention. The slab of alkali cellulose obtained from slurry-type steeping units may be advantageously treated in the manner of the invention.

Conventional alkali cellulose, shredded and aged, maybe compacted into a porous slab on a moving conveyor belt and then treated with carbon bisuliide in the method of the invention.

Alkali cellulose of a suitable degree of depolymerization for treating with CS2 on exit from the steeping operation could conveniently be made from a lowviscosity type pulp. However several means are also available for making high viscosity cellulose adaptable to such treatment. As one illustration, oxygen could be pulled into the sheet or web of alkali cellulose along with the CS2, thereby accomplishing oxidative degradation and Xanthation in one stage. Metal catalysts such as manganese and cobalt (as described in U. S. 2,542,285 and U. S. application 239,029) could be used to accelerate the alkaline oxidation reaction during xanthation or in a short aging step subsequent to steeping and prior to xanthation.

The accompanying drawings illustrate more or less diagrammatically arrangements of our apparatus for carrying out a method of our invention:

Fig. l is a sectional side view of the apparatus, and

Fig. 2 is an enlarged fragmentary view at 2-2 of Fig. 1.

Figs. l3 and 4 are sectional side views of modifications of apparatus for impregnating moving webs of alkali cellulose with carbon bisulde; and

Fig. 5 is a sectional side view of apparatus for heating Webs of alkali cellulose afterimpregnation with carbon bisuliide. Y

The apparatus comprises four principal parts, namely, the apparatus A for the impregnation of the web with caustic liquor, the sealed chamber B for the impregnation of the web with carbon bisullide, the chamber C for the removal of excess carbon bisullide, and the chamber Patented Sept. V11, 1956` D for retaining the xanthated web under elevated temperatures to complete the reaction.

The apparatus A comprises a rotatable perforated drum 1 having. a vacuum section 2 over which the web ofcellulose Apulp 3, comprising two supeiposed sheets. 4.and 5, is passed. Caustic steeping liquor of the type usually used to form alkali cellulose .is sprayed onto the web fromthe supply pipes 6. The vacuum section 2 ismaintained under a reduced pressure by a vacuum pump, not shown, connected to the pipe 7, and the liquor flows through the web in the relative volume as indicated by the shaded area within the curve 9. The impregnated web passes between the perforated drum 1 and the press roller which has a vacuum section 9 embracing the area of contact. The excess caustic liquor is removed from the web by the conjoint action of pressure and vacuum and with a minimum of compacting of the alkali cellulose. The cellulose is not only steeped in a very uniform manner but the excess liquor is effectively and uniformly removed without severely compacting the soft web.

The continuously moving web passes between the seal- .ing rollers 12 and 14 and into the sealed chamber B. These rollers are preferably formed of a spongy or otherwise soft rubber which envelop and effectively seal the area of entrance of the web into chamber B. It will be noted that the bearings 15 which support the shafts of the rollers are enclosed within the chamber and that arcuate plates 16 and 17 bear against the rollersand seal them to the wall of the chamber. The rotary shears 11 comprise two rollers, each having a multiplicity of round shear blades that slit the web in any desired number of strips. These shear rollers are alternative and may be removed when it is desired not to slit the web. After passing through the shears 11, if used, the two contacting sheets of the webV pass over the spacing bar 18 and are held apart so that liquid carbon bisuliide may be sprayed against the inner opposing faces of the sheets through the perforated pipe 19.

In View of the relatively weak character of the web, it is supported by a number of freely rotatable non-corrosive rollers 22. Itwill be noted that the sheets of the web come together shortly after passingl beyond the pipe 19 and are in contact by the time they pass through the soft rubber sealing rollers 23 and 24. The web enters chamber C and passes between the upper and lower vacuum chambers 25 and 26 which have perforated plates or shoes bearing against the upper and lower surfaces of the web through which the excess carbon bisulfide is removed. The web then passes between the sealing rollers 27 and 28 which are similar to rollers 12 and 14 and then into chamber D. In this chamber, the web first passes over guide roller 29 and then over a plurality of upper guide rollers 30 and lower guiderollers 31. Any desired number of such rollers may be used to provide the required number of convolutions or folds of the web to delay its passage sufficiently to permit completion of the xanthation reaction. These rollers may be freely rotatable or power driven by any suitable means (not shown). The web then passes over the guide roller 32 and then between the soft rubber sealing rollers 33 and 34 which are also preferably similar to the sealing rollers 12 and 14. The web of cellulose xanthate, whether in a sheet or longstrips, is dumpedk into a chamber for conversion into viscose. `The web in chamber D may be heated in any convenient manner, such as by the infrared heaters 35, which are placed between the folds of the web. Steam coils or resistant heaters may be used for the same purpose.

Chambers B and C may be consolidated into a single chamber if desired and operated at any practical pressure. These chambers may be connected to a vacuum pumptnot shown) by the .pipes ,37 andl operated at a pressure slightly belowatmospheric pressure to minimize the escape of carbon bisulfide. The chamber D may also be operated under a slightly reduced pressure by con. necting the pipe 38 to a vacuum pump. The carbon bi sulde removed from chambers B, C and D and the vacuum members 25 and 26 may be pumped through a xanthation chamber for the absorption of the carbon bisullide vapors in a batch of liuffy alkali cellulose, or it may be recovered in an activated carbon absorption unit and returned to the process.

It is to be understood, of course, that the chambers B, C and D are sealed only to exclude or retain gases under a very slight pressure difference. The sealing may not be absolute since we contemplate a certain amount of permissible leakage as by allowing some air to seep in around the rollers to prevent an escape of carbon bisulfide.

The apparatus of Fig. 3 comprises a single enclosed chamber B--C with sealing rollers 40-41 at the end where the web of alkali cellulose 3 enters and sealing rollers 42--43 where the web leaves. The two sheets 4 and 5 are separated and treated with carbon bisulde as in Fig. l. The web. is supported from below by the endless screen .44 which travels as a belt, and may be slit into strips by passing through the rotary shears 45. The excess carbon bisulfide is pulled through the sheets by thevacuum members 46-47. Member 46 is directly over the endless. screen 49 and member 47 is directly under screen 44 and the web is accordingly supported on both sides while under vacuum. The entire chamber B-C` may be. operated Yunder sub-atmospheric pressure by connecting the pipe 50 to a vacuum pump.

vThe apparatus of Fig. 4 comprises a single enclosed chamber B-C, sealing rollers 40-41, 42-43, vacuum pump 50, endless screen 44 and vacuum member 47 as in Fig. 4. The web 3 of alkali cellulose consisting of sheets4 and 5 passes under the perforated pipe 52 and is showered with carbon bisulfide just in advance of the vacuumkmember. The carbon bisulflde is pulled through the web by the vacuum, the excess enteringthe vacuum system.

Fig. 5 illustrates a modified treating chamber D having sealing rollers at the web entering and exiting ends and a pipe 51 for operatingthe chamber under a rcduced pressure. When this chamber D is operated in combination with a chamber B-C of Fig. 3 or 4, the sealingrollersy 42-43 and end wall can form the entering sealing rollers and wall of chamber D.

The web 3 which had been impregnated with carbon bisulde as in Figs.I l, 2 and 3, passes between electronic heating devices 52.

The invention very materially increases the efficiency of xanthation due to several factors. First of all, the alkali cellulose is relatively free of excess alkali and is in a relatively loose or porous state in contrast to the compacted mass of alkali cellulose usually resultingjfrom `compression to squeeze out the excess caustic. The xanthation is very efficient and can be carried lout in a shorter time on a much less bulky material than the shredded alkali cellulose and with at least equal effectiveness. It eliminates the rcumbersome and bulky equipment now necessary.

We claim:

l. In the production of viscose in which a continuously moving web of. cellulose pulp is treated with caustic liquor to form. alkalicellulose, vthe improvement which comprises uniformly converting the cellulose to alkali cellulose and passingthe web of alkali cellulose into a sealed chamber and uniformly impregnating the web with carbon bisulde by applying the carbon bisulide tothe exterior of the weband sucking it through the web by means of a vacuum toV form cellulose xanthate, reacting the carbon bisulde with the alkali cellulose for a time and at a temperature sufficient to effect uniform conversion to cellulose xanthate, vand discharging the cellulose xanthate from the systemffor conversion into viscose.

2. In the method of claim 1, slitting the web of alkali cellulose into a multiplicity of narrow strips before impregnation with carbon bisulde.

3. In the method of claim 1, passing the web after impregnation with carbon bisulde in delayed passage through an enclosed heated chamber to eect completion of the xanthation reaction.

4. In the method of claim 1, passing a plurality of superposed sheets of cellulose through the operation as a single web, separating the sheets in a sealed chamber and spraying the inner opposing faces of the sheets with carbon bisulfide, and promptly closing the sheets to trap the carbon bisulde therebetween.

5. According to the method of claim 1 in which the web of alkali cellulose, uniformly impregnated with carbon bisulde is heated electronically to effect rapid conversion to cellulose Xanthate.

6. In the production of viscose in which a contnuously moving web of cellulose pulp is treated with caustic liquor to form alkali cellulose, the improvement which `comprises uniformly converting the cellulose to alkali cellulose and passing the web of akali cellulose into a sealed chamber and sucking carbon bisulide into the web of alkali cellulose, thereby uniformly impregnating the web with carbon bisulde to form cellulose Xanthate, slitting the web of cellulose Xanthate into narrow strips, and passing the carbon bisullide impregnated slit strips into a wet churn to eilect a completion of the Xanthation reaction.

7. In the production of viscose in which a plurality of superposed sheets of alkali `cellulose are passed through the operation as a web of indefinite length the improvement which comprises applying a predetermined dosage of carbon bisulde to one surface of the web while simultaneously applying a vacuum to the opposite surface of the web to draw the carbon bisuliide uniformly into the web.

8. In the production of viscose in which a continuously moving web of cellulose pulp is treated with caustic soda liquor to form a web of alkali cellulose, the improvement which comprises passing the web of alkali cellulose into a Sealed chamber, applying a predetermined dosage of carbon bisulde to the top surface of the web While simultaneously applying vacuum to the under surface of the web to distribute the carbon bisulide uniformly on the fibers within the web, reacting the carbon bisulfide with the alkali cellulose to form cellulose xanthate, and discharging the cellulose Xanthate from the system for dissolving into viscose.

References Cited in the iile of this patent UNITED STATES PATENTS 520,770 Cross et al lune 5, 1894 765,508 Noyes July 19, 1904 1,672,249 Ellis June 5, 1928 1,884,486 Zavertnik Oct. 25, 1932 1,892,579 Kilner Dec. 27, 1932 2,011,156 Nelson Aug. 13, 1935 2,092,306 Fuelnegg et al. Sept. 9, 1937 2,122,519 Dokkum Juiy 5, 1938 2,126,044 Rolleston Aug. 9, 1938 2,384,298 Green Sept. 4, 1945 2,530,403 Seaman Nov, 21, 1950 

1. IN THE PRODUCTION OF VISCOSE IN WHICH A CONTINUOUSLY MOVING WEB OF CELLULOSE PULP IS TREATED WITH CAUSTIC LIQUOR TO FORM ALKALI CELLULOSE, THE IMPROVEMENT WHICH COMPRISES UNIFORMLY CONVERTING THE CELLULOSE TO ALKALI CELLULOSE AND PASSING THE WEB OF ALKALI CELLULOSE INTO A SEALED CHAMBER AND UNIFORMLY IMPREGNATING THE WEB WITH CARBON BISULFIDE BY APPLYING THE CARBON BISULFIDE TO THE EXTERIOR OF THE WEB AND SUCKING IT THROUGH THE WEB BY MEANS TO A VACUNM TO FROM CELLULOSE XANTHATE, REACTING THE CARBON BISULFIDE WITH THE ALKALI CELLULOSE FOR A TIME AND AT A TEMPERATURE SUFFICIENT TO EFFECT UNIFORM CONVERSION TO CELLULOSE XANTHATE, AND DISCHARGING THE CELLULOSE XANTHATE FROM THE SYSTEM OF CONVERSION INTO VISCOSE. 